Our research has recently uncovered evidence for the presence of 2 new myelin enzymes: CDP-ethanolamine:1,2-diacyglycerol ethanolamine-phosphotransferase and CDP-choline:1,2-diacyglycerol cholinephosphotransferase. Work in progress has demonstrated that these are true myelin enzyme, distinct from their microsomal counterparts. A full characterization of these enzymes will be undertaken to define kinetic parameters, cofactor requirements, developmental changes and distribution within myelin subfractions. A start will be made toward isolating the 2 enzymes as homogeneous proteins. Selective lipid biosynthetic activity in myelin had previously been suggested by in vivo experiments of our group which demonstrated uptake of serine from the axon and incorporation into specific lipids (but not proteins). That study suggested the probable existence of several additional lipid-synthesizing enzymes in myelin; a systematic search for such enzymes will be carried out using the labeling pattern of the in vivo experiment as a guide. The transaxonal phenomenon will be further investigated to determine whether the axon is a common (and possible obligatory) source of substrate for certain of the myelin enzymes. To the degree that such results are affirmative the enzymes in question will be tentatively viewed as potential participants in a form of axon-glial interaction, and experiments will then be developed to test the hypothesis.